Serious deep mycosis such as invasive candidiasis can be often a fatal disease. It has been considered that a principal defense mechanism of a host organism against fungi such as candida originally owes to nonspecific immunity by neutrophils. So long as this defense mechanism functions normally, the risk of infection by fungi is limited. However, in recent years, the risk of developing deep mycosis has increased due to an increase in the number of patients with underlying diseases compromising the immune system of the organism, such as malignant tumors or AIDS, overuse of anticancer drugs or immunosuppressive drugs, heavy use of antibacterial antibiotic substances or steroid hormones and long-term use of intravenous hyperalimentation or venous catheterization (Non-Patent Document 1).
Only 7 agents for such deep mycosis are known, namely, amphotericin B, flucytosine, miconazole, fluconazole, itraconazole, micafungin and voriconazole. Amphotericin B has very strong fungicidal action, but its clinical use is limited due to a problem of side effects, for example, nephrotoxicity. Flucytosine has a problem of development of tolerance and is rarely used alone today. Micafungin has weak activity against Cryptococcus spp. Other agents are generically called azole antifungal agents and are most frequently used now owing to the favorable balance between efficacy and safety, although their fungicidal actions tend to be in general inferior to that of amphotericin B (Non-Patent Document 2).
Recently, fluconazole-resistant Candida albicans have been detected at high frequency derived from oropharyngeal candidiasis of AIDS patients, who have received repeated-dose administration of fluconazole. Furthermore, many of the resistant strains show cross-resistance to itraconazole and other azole agents. Further, isolation of resistant strains from non-AIDS patients, who have developed chronic mucocutaneous candidiasis or deep candidiasis, has been reported (Non-Patent Document 3). The issue of the resistance has a serious impact on management of rapidly increasing patients with deep mycosis (Non-Patent Document 3).
On the other hand, an arylamidine derivative having an antifungal activity is known (Patent Documents 1 and 2).    Patent Document 1: WO-A-03-074476    Patent Document 2: WO-A-2006-003881    Non-Patent Document 1: Rinsho to Biseibutsu (Clinics and Microorganisms), vol. 17, p. 265-266, 1990    Non-Patent Document 2: Rinsho to Biseibutsu (Clinics and Microorganisms), vol. 21, p. 277-283, 1994    Non-Patent Document 3: Rinsho to Biseibutsu (Clinics and Microorganisms), vol. 28, p. 51-58, 2001